This invention relates generally to seals and particularly to a seal arrangement for sealing liquid in a chamber at a level above the height of a strip passing through the chamber.
Many thin metal items, such as shadow masks for color picture tubes, are made by acid etching. In acid etching, a pattern of the part to be etched is photographically produced on a photoresist material which is coated onto the metal. The photoresist material is exposed to light through a transparent material bearing the opaque pattern. The unexposed portion of the photoresist material is washed away leaving bare metal along the pattern, while the exposed material protects the metal from the acid. Typically, a large number of the patterns are photographically produced on a long strip of metal which is horizontally pulled through an acid etch tank. The acid in the tank etches through the bare metal to produce the desired part. Frequently, the pattern is produced on both sides of the metal strip and the etching occurs from both sides.
The metal strip moves continuously through the etch tank. After etching is completed and the strip exits from the tank, a large amount of acid clings to the photoresist material on both sides of the strip. It is essential that this acid be removed as soon as possible. Typically, the acid is removed by spraying the strip with a rinsing solution in a spray chamber. However, when the etched pattern contains a large number of small apertures, rinsing solution does not fully enter the apertures. Because of the importance of complete cessation of acid etching immediately after the strip leaves the etch tank, it is preferrable to have a rinsing chamber in which the strip is completely submersed in liquid located in the closest possible proximity of the etch tank exit. This has been difficult in the past because the liquid in the rinsing chamber must pass over both sides of the strip and therefore the liquid level in the chamber must be higher than the strip. The strip, therefore, must pass either over or through the sides of the chamber making it very difficult to seal the rinsing liquid in the chamber. For these reasons, there is a need for a seal arrangement for retaining liquid in a chamber at a level higher than the height of the strip being rinsed. The liquid level must, therefore, also be higher than some of the sides of the chamber, whereby a horizontal strip of material can be pulled through the liquid with the liquid flowing over both sides of the strip. The present invention fulfills this long felt need.